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253
iTechSharp/srcbc/crypto/modes/CtsBlockCipher.cs
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253
iTechSharp/srcbc/crypto/modes/CtsBlockCipher.cs
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using System;
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using System.Diagnostics;
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using Org.BouncyCastle.Crypto;
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using Org.BouncyCastle.Crypto.Parameters;
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namespace Org.BouncyCastle.Crypto.Modes
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{
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/**
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* A Cipher Text Stealing (CTS) mode cipher. CTS allows block ciphers to
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* be used to produce cipher text which is the same outLength as the plain text.
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*/
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public class CtsBlockCipher
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: BufferedBlockCipher
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{
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private readonly int blockSize;
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/**
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* Create a buffered block cipher that uses Cipher Text Stealing
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*
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* @param cipher the underlying block cipher this buffering object wraps.
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*/
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public CtsBlockCipher(
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IBlockCipher cipher)
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{
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// TODO Should this test for acceptable ones instead?
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if (cipher is OfbBlockCipher || cipher is CfbBlockCipher)
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throw new ArgumentException("CtsBlockCipher can only accept ECB, or CBC ciphers");
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this.cipher = cipher;
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blockSize = cipher.GetBlockSize();
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buf = new byte[blockSize * 2];
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bufOff = 0;
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}
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/**
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* return the size of the output buffer required for an update of 'length' bytes.
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*
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* @param length the outLength of the input.
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* @return the space required to accommodate a call to update
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* with length bytes of input.
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*/
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public override int GetUpdateOutputSize(
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int length)
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{
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int total = length + bufOff;
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int leftOver = total % buf.Length;
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if (leftOver == 0)
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{
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return total - buf.Length;
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}
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return total - leftOver;
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}
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/**
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* return the size of the output buffer required for an update plus a
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* doFinal with an input of length bytes.
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*
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* @param length the outLength of the input.
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* @return the space required to accommodate a call to update and doFinal
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* with length bytes of input.
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*/
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public override int GetOutputSize(
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int length)
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{
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return length + bufOff;
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}
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/**
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* process a single byte, producing an output block if neccessary.
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*
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* @param in the input byte.
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* @param out the space for any output that might be produced.
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* @param outOff the offset from which the output will be copied.
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* @return the number of output bytes copied to out.
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* @exception DataLengthException if there isn't enough space in out.
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* @exception InvalidOperationException if the cipher isn't initialised.
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*/
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public override int ProcessByte(
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byte input,
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byte[] output,
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int outOff)
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{
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int resultLen = 0;
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if (bufOff == buf.Length)
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{
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resultLen = cipher.ProcessBlock(buf, 0, output, outOff);
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Debug.Assert(resultLen == blockSize);
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Array.Copy(buf, blockSize, buf, 0, blockSize);
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bufOff = blockSize;
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}
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buf[bufOff++] = input;
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return resultLen;
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}
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/**
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* process an array of bytes, producing output if necessary.
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*
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* @param in the input byte array.
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* @param inOff the offset at which the input data starts.
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* @param length the number of bytes to be copied out of the input array.
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* @param out the space for any output that might be produced.
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* @param outOff the offset from which the output will be copied.
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* @return the number of output bytes copied to out.
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* @exception DataLengthException if there isn't enough space in out.
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* @exception InvalidOperationException if the cipher isn't initialised.
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*/
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public override int ProcessBytes(
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byte[] input,
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int inOff,
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int length,
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byte[] output,
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int outOff)
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{
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if (length < 0)
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{
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throw new ArgumentException("Can't have a negative input outLength!");
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}
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int blockSize = GetBlockSize();
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int outLength = GetUpdateOutputSize(length);
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if (outLength > 0)
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{
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if ((outOff + outLength) > output.Length)
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{
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throw new DataLengthException("output buffer too short");
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}
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}
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int resultLen = 0;
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int gapLen = buf.Length - bufOff;
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if (length > gapLen)
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{
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Array.Copy(input, inOff, buf, bufOff, gapLen);
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resultLen += cipher.ProcessBlock(buf, 0, output, outOff);
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Array.Copy(buf, blockSize, buf, 0, blockSize);
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bufOff = blockSize;
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length -= gapLen;
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inOff += gapLen;
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while (length > blockSize)
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{
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Array.Copy(input, inOff, buf, bufOff, blockSize);
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resultLen += cipher.ProcessBlock(buf, 0, output, outOff + resultLen);
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Array.Copy(buf, blockSize, buf, 0, blockSize);
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length -= blockSize;
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inOff += blockSize;
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}
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}
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Array.Copy(input, inOff, buf, bufOff, length);
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bufOff += length;
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return resultLen;
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}
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/**
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* Process the last block in the buffer.
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*
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* @param out the array the block currently being held is copied into.
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* @param outOff the offset at which the copying starts.
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* @return the number of output bytes copied to out.
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* @exception DataLengthException if there is insufficient space in out for
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* the output.
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* @exception InvalidOperationException if the underlying cipher is not
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* initialised.
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* @exception InvalidCipherTextException if cipher text decrypts wrongly (in
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* case the exception will never Get thrown).
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*/
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public override int DoFinal(
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byte[] output,
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int outOff)
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{
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if (bufOff + outOff > output.Length)
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{
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throw new DataLengthException("output buffer too small in doFinal");
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}
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int blockSize = cipher.GetBlockSize();
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int length = bufOff - blockSize;
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byte[] block = new byte[blockSize];
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if (forEncryption)
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{
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cipher.ProcessBlock(buf, 0, block, 0);
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if (bufOff < blockSize)
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{
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throw new DataLengthException("need at least one block of input for CTS");
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}
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for (int i = bufOff; i != buf.Length; i++)
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{
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buf[i] = block[i - blockSize];
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}
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for (int i = blockSize; i != bufOff; i++)
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{
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buf[i] ^= block[i - blockSize];
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}
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IBlockCipher c = (cipher is CbcBlockCipher)
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? ((CbcBlockCipher)cipher).GetUnderlyingCipher()
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: cipher;
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c.ProcessBlock(buf, blockSize, output, outOff);
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Array.Copy(block, 0, output, outOff + blockSize, length);
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}
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else
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{
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byte[] lastBlock = new byte[blockSize];
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IBlockCipher c = (cipher is CbcBlockCipher)
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? ((CbcBlockCipher)cipher).GetUnderlyingCipher()
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: cipher;
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c.ProcessBlock(buf, 0, block, 0);
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for (int i = blockSize; i != bufOff; i++)
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{
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lastBlock[i - blockSize] = (byte)(block[i - blockSize] ^ buf[i]);
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}
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Array.Copy(buf, blockSize, block, 0, length);
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cipher.ProcessBlock(block, 0, output, outOff);
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Array.Copy(lastBlock, 0, output, outOff + blockSize, length);
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}
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int offset = bufOff;
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Reset();
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return offset;
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}
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}
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}
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